From: Viresh Kumar <viresh.kumar@linaro.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael Wysocki <rjw@rjwysocki.net>,
Ingo Molnar <mingo@redhat.com>,
linaro-kernel@lists.linaro.org, linux-pm@vger.kernel.org,
linux-kernel@vger.kernel.org,
Vincent Guittot <vincent.guittot@linaro.org>,
Juri Lelli <Juri.Lelli@arm.com>,
Robin Randhawa <robin.randhawa@arm.com>,
Steve Muckle <smuckle.linux@gmail.com>,
tkjos@google.com, Morten Rasmussen <morten.rasmussen@arm.com>
Subject: Re: [PATCH] cpufreq: schedutil: add up/down frequency transition rate limits
Date: Mon, 21 Nov 2016 17:00:16 +0530 [thread overview]
Message-ID: <20161121113016.GD10014@vireshk-i7> (raw)
In-Reply-To: <20161121111243.GK3102@twins.programming.kicks-ass.net>
On 21-11-16, 12:12, Peter Zijlstra wrote:
> I think it should be replaced by a value provided by the driver. It
> makes sense to have a rate-limit in so far as that it doesn't make sense
> to try and program the hardware faster than it can actually change
> frequencies and/or have a programming cost amortization. And this very
> clearly is a driver specific thing.
We already have something called as transition_latency for that (though it isn't
used much currently).
> It however doesn't make sense to me to fudge with this in order to
> achieve ramp up/down differences.
So if a platform, for example, can do DVFS in say 100-500 us, then the scheduler
should try to re-evaluate frequency (and update it) after that short of a
period? Wouldn't that scheme waste lots of time doing just freq updates? And
that's the primary reason why cpufreq governors have some sort of sampling-rate
or rate-limit until now.
--
viresh
next prev parent reply other threads:[~2016-11-21 11:30 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-17 5:18 [PATCH] cpufreq: schedutil: add up/down frequency transition rate limits Viresh Kumar
2016-11-21 10:08 ` Viresh Kumar
2016-11-21 10:19 ` Peter Zijlstra
2016-11-21 10:48 ` Viresh Kumar
2016-11-21 11:12 ` Peter Zijlstra
2016-11-21 11:30 ` Viresh Kumar [this message]
2016-11-21 11:48 ` Peter Zijlstra
2016-11-21 12:14 ` Juri Lelli
2016-11-21 12:26 ` Peter Zijlstra
2016-11-21 13:53 ` Juri Lelli
2016-11-21 14:17 ` Peter Zijlstra
2016-11-21 14:37 ` Juri Lelli
2016-11-21 14:43 ` Peter Zijlstra
2016-11-21 14:59 ` Juri Lelli
2016-11-22 9:27 ` Vincent Guittot
2016-11-22 11:03 ` Patrick Bellasi
2016-11-21 14:59 ` Patrick Bellasi
2016-11-21 15:26 ` Peter Zijlstra
2016-11-21 15:34 ` Peter Zijlstra
2016-11-21 16:24 ` Patrick Bellasi
2016-11-21 16:46 ` Peter Zijlstra
2016-11-21 20:53 ` Rafael J. Wysocki
2016-12-29 3:24 ` Wanpeng Li
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